The present invention is situated in the field of reconfigurable electromagnetic antennas.
The proliferation of wireless and mobile applications, in a radiofrequency signal propagation environment constrained by multiple interference and signal attenuation phenomena, requires a great adaptation of the terminals with minimum impact on, among other things, the complexity, the size, the weight, the autonomy or even the cost of these terminals.
The development of reconfigurable electromagnetic antennas for these terminals hopes to overcome these constraints.
There are several types of reconfigurable antennas. For example, there are antennas that can be reconfigured in frequency, antennas that can be reconfigured in polarization or even antennas that can be reconfigured in radiation pattern.
An antenna that can be reconfigured in frequency can adapt its radiation frequency and sweep a wide frequency spectrum. Such an antenna makes it possible, among other things, to receive on one and the same terminal several signals each satisfying a different standard.
An antenna that can be reconfigured in polarization can modify its polarization state (horizontal, vertical, circular or even elliptical) to maximise the received or transmitted signal power.
An antenna that can be reconfigured in radiation pattern can modify its radiation pattern to adapt its directivity to a propagation environment in order, for example, to limit the interference phenomena.
In the current state of the art, given in particular the size constraints of the terminals, the reconfiguration of an antenna is not obtained by a mechanical or physical deformation of the antenna or its component elements.
Currently, the reconfiguration of an antenna can be obtained by switching certain conductive elements of which it is composed (radiating element, dielectric, ground plane).
The reconfiguration of an antenna can also be obtained by having impedances connected to certain points of the antenna varied.
These two reconfiguration modes present drawbacks.
In the case where elements of the antenna are switched, a discontinuous variation of the properties (frequency, polarization, radiation pattern) that are to be made to evolve is obtained.
In the case where impedances connected to certain points of the antenna are made to vary, a continuous variation of the frequency or of the radiation pattern is obtained, but it is limited by the variation ranges of the impedances used.
Furthermore, the devices used for the reconfiguration (switches and impedances) present intrinsic losses that affect the effectiveness of the antenna.
The patent application US 2004/0252069 presents a dynamically reconfigurable antenna with characteristics that can vary.
The radiating element of this antenna comprises a conductive fluid contained in a cavity. This antenna also comprises a fluid control system that makes it possible to selectively add or remove fluid to or from the cavity, this causing the size of the radiating element to be varied.
There is therefore a real need of a technique for reconfiguring an electromagnetic antenna that does not present the abovementioned drawbacks of the known reconfiguration techniques.